2.1. Immunochromatographic Assay Devices
Immunochromatographic assays using a membrane as a solid support in a dipstick or flow-through device are now established for use in the clinical laboratory and for alternative, i.e., non-laboratory, site testing. Assays using this type of format are available for drugs of abuse (cocaine, cannabinoid, amphetamines, opiates, PCP), pregnancy and fertility (hCG and hLH, respectively), and infectious diseases (chlamydia, Strep A, infectious mononucleosis (IM)).
The usual presentation for an immunochromatographic assay device is a membrane (cellulosic or non-cellulosic) enclosed in a plastic holder. This device is further packaged singly or in bulk in a sealed foil or plastic pouch, which acts as an environmental control. Package integrity is essential for extended stability of the device at room temperature.
The plastic holder keeps the membrane in a suitable configuration in order to ensure correct functioning of the entire device. There are usually 1-3 windows in the holder. There is always a test window which serves to allow observation of the result. The test window may also allow for viewing of a control reaction, e.g., to confirm adequate performance of the test; alternatively, the control window may be separate from the result window. Additionally there may be a third window that allows application of the liquid sample to the membrane, either by direct placement of the device in the sample (allowing contact of the sample at the open window), or by application of the sample with a dropper at the window. The plastic holder also usually holds the membrane in contact with pads (cellulosic or non-cellulosic) which serve as wicks. Usually there is an applicator pad at the sample application window or at the site where the sample is applied, and a pad at the opposite end of the membrane. The plastic holder keeps the pad(s) in contact with the membrane, thus providing a continuum for wicking of sample from the applicator up through the membrane and from the application pad to the top pad.
There are many variations of the basic structure of assay devices. For example, Litman et al. (U.S. Pat. Nos. 5,156,952 and No. 5,030,558) describe an assay method and device for determining the presence of a minimum amount of an analyte in a sample. Ullman et al. (U.S. Pat. Nos. 5,137,808 and 4,857,453) describe an device to house an assay membrane that includes self-contained liquid reagents to aid sample flow. Dafforn et al. (U.S. Pat. No. 4,981,768) describes a device with ports for applying sample and extra liquid. Assay devices are also described by Corti et al. (European Patent Application No. 89118378.2), Greenquist et al. (U.S. Pat. No. 4,806,312) and Berger et al. (U.S. Pat. No. 5,114,673).
The plastic device containing the membrane and pads is usually packaged in a sealed foil or plastic pouch with or without desiccant. The outer packaging pouch is essential as an environmental control, particularly to limit exposure of the membrane strip to the external environment and to ensure integrity of the test. Low humidity within the package is important essential for extended room temperature stability of the device, thus a desiccant is usually present. The addition of a moisture indicator inside the sealed package, or integral to the device, insures integrity of the device before use.
The usual test procedure involves opening the outer packaging and removal of the plastic device, application of the sample at the sample window (by dipping the device into the sample, or by dropping the sample onto the sample window), waiting the recommended time for running the assay, and checking the result window for a positive or negative result and the control window to determine whether the test proceeded correctly.
The packaging required for test devices present certain drawbacks. For example, if the devices are packaged in bulk, any breach of the packaging, whether by an accidental tear or to retrieve a device for a test, will limit the shelf life of the devices. Individual packaging of each test device is expensive, and produces additional solid waste for disposal.
Thus, it is the object of the present invention to provide an integrated packaging-holder immunochromatographic assay device. It is a further object to provide a device that eliminates the need for a separate plastic holder and outer packaging.